BACKGROUND: It is controversial whether or not pregnant bitches become sensitized to red blood cell (RBC) antigens. HYPOTHESIS: Bitches do not develop alloantibodies to RBC antigens during gestation and can be used safely as blood donors. ANIMALS: The study group included 35 healthy female dogs with a prior history of 1 (n = 12), 2 (n = 14), or >or= 3 (n = 9) pregnancies. The control group consisted of 15 healthy female dogs without any history of pregnancy. METHODS: All dogs were blood typed for dog erythrocyte antigens (DEA) 1.1, 1.2, 3, 4, 5, and 7 using ethylenediaminetetraacetic acid blood samples and polyclonal antisera. Antibody screening was performed with serum and canine RBC panels of known blood type. An autocontrol and direct antiglobulin test were performed to rule out the presence of autoantibodies. RESULTS: The only alloantibodies identified were those against DEA 7 and the prevalence of anti-DEA 7 alloantibodies was similar in dogs with known history of pregnancy (11.4%) and in the control group (13.3%). CONCLUSIONS AND CLINICAL IMPORTANCE: These results confirm previous studies and clinical transfusion medicine experience. Naturally occurring anti-DEA 7 alloantibodies have been reported but their clinical relevance has not been shown. Pregnancy does not appear to sensitize dogs to RBC antigens. Consequently, dogs with prior history of pregnancy can be used safely as blood donors. Conversely, no additional pretransfusion compatibility studies would be required should these dogs themselves need to be transfused.